with a pipe,i could see it being useful.some people say with a stock machine it isn't worth it.when i put it on my quad when it was stock,it seemed to be more snappy on the throttle.(rev quicker).i would suggest geting one but i'm sure the wb rev kit is the same as the stock honda xr 400 rev box.all white bros does is carve their initals on the stock box and call it their own for about $50 more.i would hold off until someone else comfirms that for sure.i know for sure that the boxes are the same except for the price but i'm not sure if it is the xr 400 box or another machine i wish i would have known all of this before i spent the $109:grr instead of $60.
UPDATE:someone else posted it is the xr 250 rev box and the prices are correct.